1. Field of the Invention
The invention relates to a scanner device for positioning a driven deflection mirror. The invention may be applied in the laser material processing e. g. for positioning a laser beam.
2. Description of the Related Art
Scanner devices or optical scanners are used to position light beams by deflection and e.g. to generate modulation pattern. An optical scanner may comprise a moving coil, a rotary magnet or a moving iron drive for repositioning the deflection mirror. Said mirror is mounted on a shaft and the shaft, and thus the mirror, is pivotable by means of the respective drive. It can, for example, be provided, to adjust and stabilize the rotation angle of the mirror by means of a feedback provided by an angle encoder, which, for example, is directly coupled to the shaft of the drive, and a corresponding control electronics.
Moving coil drives have a smaller moment of inertia compared to rotary magnet drives of the same torque constant due to a lower weight of the coil. Since the coil is surrounded by air, however, there is a poor heat dissipation from the coil to the environment, so that only a small permanent force can be generated. In addition, the supply of power is subject to wear and is accompanied by parasitic mechanical losses. In rotary magnet drives the coil may be in contact with a magnetic yoke, so that the heat generated by the coil can be dissipated via the magnetic yoke to the environment; however, the mass of the magnets is increasing when the producible torque shall be raised. On the other hand, moving iron drives utilize a soft iron element as a rotor, wherein the rotary movement of the soft iron element results in a change of the resistance within the magnetic circuit, which, for example, may be generated by a coil enclosing an iron core.
The U.S. Pat. No. 5,225,770 A for example discloses an optical scanner having a rotary magnet drive, which exerts forces on a permanent magnet rotor by means of fixed, in a soft iron yoke embedded coils, wherein at one end of the rotor, a mirror is mounted and at the other end of the rotor, a position detector is arranged.
In material processing by a laser beam, the used small beam diameter and the required short dwell times of the beam result in high demands on the positioning of the mirror and its speed of positioning, i. e. a fast and accurate repositioning of the deflection mirror from one angular position to another angular position is required. However, a fast and accurate repositioning of the deflection mirror requires a small torque of inertia (in comparison to the drive torque) as well as a stiff connection between drive and mirror, wherein in the case of optical scanner devices with a mirror mounted to a shaft, which is driven by a drive, the torque of inertia of the system to be moved by the shaft is determined by the mirror while the connecting rigidity is limited by the torsion of the torque-transmitting shaft.